Antenna circuits are implemented, for example, in transponders for different applications. A transponder is usually a small-sized equipment which comprises an antenna circuit. The antenna circuit usually comprises a resonance circuit and may also comprise an antenna, or eg the coil of the resonance circuit operates as an antenna. The transponder may further comprise a chip to/from which information can be wirelessly stored/read. The information is stored into a memory of the chip or generated e.g. by a logical circuit of the chip upon request. The energy is usually externally provided to the transponder by the reader when information is to be stored into or read from the chip. The energy is supplied to the transponder as a radio frequency (RF) energy. The antenna of the transponder receives the energy. The antenna is part of the resonance circuit wherein the energy must have a certain frequency. In the transponder the received energy is usually stored to an energy storage such as a capacitor. The stored energy suffices for the information storage/reading operation when the resonance circuit and the transmission frequency of the reader are near each other i.e. the resonance circuit is tuned to the transmission frequency of the reader.
There are different systems in which transponders are utilized. However, the transmission frequencies are not the same in every system. Therefore, different resonance frequencies are needed in transponders of different systems. Moreover, tolerances in the manufacturing processes of the transponders can affect that the resonance frequencies need to be tuned before the transponder is ready for use. For example, the input impedance of the chip may vary in different production batches. Further, the input impedances of the chips of different manufacturers may vary so largely that similar chips from different manufacturers can not be used with the same antenna circuit. Also the coil/antenna manufacturing and chip assembly processes may affect variations in the joint impedances which affect the resonance frequency of the transponder.
There are also other factors which may affect the resonance frequency of the transponder. For example when the transponder is placed into a housing the material of the housing may change the resonance frequency. Further, the application in which the transponder will be used may affect to the resonance frequency. Some materials such as plastics have more effect to the resonance frequency than some other materials such as cardboard. When the transponder is operating at UHF area (Ultra High Frequencies) the resonance frequency may drop about 50-100 MHz on plastic application or about 10-20 MHz on cardboard application. The same phenomenon exists also on transponders operating at HF frequencies.
There are some prior art tuning methods in which the inductance of the coil of the resonance circuit is changed by mechanically altering the coil. For example, a coil may have a number of short-circuits which can be broken to change the inductance of the coil. Hence, the transponder is measured and if it is not in resonance, one short-circuit is broken. After that the resonance frequency is measured again and another short-circuit is broken if necessary. This kind of tuning method is time consuming and needs extra production steps.
Another drawback in prior art is that the same antenna and/or coil can not be used in different kinds of systems but each system needs a specific antenna and/or coil.
SUMMARY OF THE INVENTION
The present invention provides an improved method for tuning the resonance frequency of the resonance circuit, an antenna circuit, and a transponder. The invention is based on the idea that the antenna circuit is provided with multiple of connection areas for a component such as a chip so that at least two such connection areas result a different resonance frequency when the component is assembled to such connection areas. Therefore, the selection of connection areas for connecting a component to the antenna circuit can be used to select the resonance frequency for the antenna circuit. To put it more precisely, the manufacturing method according to the present invention is primarily characterised in that the method comprises forming a multiple of connection areas for connecting a component to the antenna circuit, at least two of said multiple of connection areas being part of the resonance circuit. The tuning method according to the present invention is primarily characterised in that the antenna circuit comprises a multiple of connection areas for connecting a component to the antenna circuit, at least two of said multiple of connection areas being part of the resonance circuit, wherein the method comprises selecting at least one connection area for the chip amongst said at least two of said multiple of connection areas. The antenna circuit according to the present invention is primarily characterised in that the antenna circuit further comprises a multiple of connection areas for connecting a component to the antenna circuit the component comprising a component impedance, at least two of said multiple of connection areas being part of the resonance circuit. The transponder according to the present invention is primarily characterised in that the antenna circuit further comprises a multiple of connection areas for connecting the component to the transponder, at least two of said multiple of connection areas being part of the resonance circuit.
The invention provides advantages compared to prior art methods, antenna circuits and transponders. When producing the transponders according to the present invention it is not necessary to measure the resonance frequency of all the transponders of a production batch but only one or few of them because the materials and the process have a quite uniform quality. The other transponders are produced according to the measurements of the one or few samples of the transponders of the production batch. In other words, the connection areas for the chip are selected according to the measurements and all the other transponders of the same batch can be manufactured accordingly. When a different resonance frequency is needed, another connection area(s) is/are selected for the chip. The antenna circuit can comprise many connection areas in a way that the difference between the smallest and highest resonance frequency that can be achieved by the selection of the connection area of the chip can be very large. Thus, the same antenna circuits can be used in many different transponders. Therefore, bigger manufacturing volumes of similar antenna circuits can be achieved. The transponders can also be mass tailored according to the needs of customers who will use the transponders in their products, for example. One further advantage to mention is that the tuning is simpler than in prior art methods.
Same antenna circuit can be used in different technology chip attachment lines. High quality lines produce transponders with smaller parasitic capacitances, which will increase the resonance frequency. Many connection areas enable to produce optimized transponders in many production lines.